Sensing systems on a vehicle require knowledge of navigation parameters, for example, velocity, position, and orientation, of the sensors to provide accurate measurements from the sensors while the vehicle is in motion. The vehicle comprises a high performance reference navigation system, for example, a master navigation system, to provide velocity, position, and orientation of the vehicle relative to a reference navigation coordinate system. The master navigation system is mounted in the vehicle but is usually physically separated from the sensing systems. As the vehicle is in motion, the vehicle bends. The bending of the vehicle causes instantaneous discrepancies between the position expressed by the master navigation system and the position experienced by the sensor. The difference between the position expressed by the master navigation system and the position experienced by the sensor is the “lever arm error.” The lever arms between the master navigation system and the sensing systems are nominally known. As one shortcoming, due to bending of the vehicle, errors are induced into the velocity, position, and orientation of the sensing system where outputs of the master navigation system are corrected based on the nominal lever arms.
For example, in a synthetic aperture radar, an image is formed by combining signals from multiple sensors over a period of time while the radar is in motion. The lever arms between the master navigation system and the multiple sensors are nominally known. Where the vehicle bends, variations in the motion of the vehicle degrade the image. Data from the master navigation system is utilized to compensate the signals from the multiple sensors to form the image. The master navigation system employs the nominal lever arms to compensate the signals from the multiple sensors. While the vehicle is in motion, the position expressed by the master navigation system is different from the position experienced by the sensor as the master navigation system is separated from the sensing system. The difference is the lever arm error.
One prior art solution to reduce the level arm error is to employ a high performance navigation system, for example, a slave navigation system, at a location of the sensing system to provide velocity, position, and orientation of the sensing system. As another shortcoming, it is costly to add additional high performance navigation systems into the vehicle. Another prior art solution to reduce the level arm error is to employ a smaller, lightweight, lower performance navigation system, for example, a slave navigation system, at a location of the sensing system. The slave navigation system at the location of the sensing system determines the velocity, position, and orientation of the sensing system relative to a coordinate system defined by the slave navigation system at the location of the sensing system. As yet another shortcoming, the coordinate system defined by the slave navigation system at the location of the sensing system differs from the reference coordinate system defined by the master navigation system of the vehicle. Where multiple sensing systems and multiple navigation systems are employed on the vehicle, the navigation systems employ multiple reference coordinate systems. It is desirable to obtain data from the sensing systems in the same coordinate system.
Thus, a need exists for determining navigation parameters of a plurality of sensors on a vehicle relative to one coordinate system.